1. FIELD OF THE INVENTION
The present invention relates to an internal combustion engine stop device having an electrical self-holding function.
2. DISCUSSION OF BACKGROUND
FIG. 2 is a schematic circuit diagram showing the structure of a conventional internal combustion engine stop device. In FIG. 2, reference numeral 1 designates a power generation winding which is driven by an engine (not shown) to generate an a.c. output. Reference numeral 2 designates a capacitor for an ignition winding, which is charged through a diode 3 by one of the polarity outputs of the a.c. power generation winding 1. Reference numeral 4 designates an ignition coil whose secondary winding is connected to an ignition plug 5. Reference numeral 6 designates a signal winding which generates an ignition signal in synchronism with the rotation of the engine. The output of the signal winding is applied to the gate of a thyristor 8 through a diode 7. Reference numeral 9 designates a bias resistor which is connected between the gate and the cathode of the thyristor 8. Reference numeral 10 designates a diode which is connected in parallel with the primary coil of the ignition winding 4 to bypass the counter-electromotive force caused in the ignition coil 4.
Reference numeral 11 designates a self-reset type stop switch which has normally opened contacts. The switch has one terminal connected to a stop circuit 12 and the other terminal grounded. Reference numeral 13 designates a thyristor in the stop circuit 12, whose anode is connected to one end of the power generation winding 1, and whose cathode is grounded through a resistor 14 and a diode 15. The gate of the thyristor 13 is connected to the cathode of a diode 17 through a resistor 16. Between the gate and the cathode of the thyristor 13 is connected a resistor 18. Reference numerals 19 and 20 designate a diode and a capacitor, respectively, which are connected in series so as to be in parallel with the resistor 14. The junction between the diode 19 and the capacitor 20 is connected to the anode of the diode 17, and also connected to the one terminal of the stop switch through a diode 21 which is reversely connected. The junction between the capacitor 20 and the resistor 14 is connected to the one end of the power generation winding 1 through a diode 22.
In operation, when the engine rotates, the power generation winding 1 generates an a.c. output, and charges the capacitor 2 through the diode 3 by the one polarity output (b direction voltage). The signal winding 6 outputs the ignition signal corresponding to a predetermined ignition timing, thereby causing the thyristor 8 to conduct. The conduction of the thyristor 8 discharges the charge stored in the capacitor 2 to the primary winding of the ignition coil 4, causing a high voltage to generate in the primary winding. As a result, a spark discharge is caused in the ignition plug 5.
During the normal operation of the engine, the stop switch 11 is opened, and the thyristor 13 in the stop circuit 12 does not conduct. As a result, the output of the power generation winding 1 is supplied to the capacitor 2 without being brought to a short-circuit state. In this way, the normal ignition operation is carried out.
When the stop switch 11 is closed, the other polarity output (a direction voltage) generated by the power generation winding 1 flows in the route of the stop switch 11, the diode 21, the capacitor 20, the diode 22 and the power generation winding 1, thereby charging the capacitor 20. When the power generation winding 1 generates the b direction voltage output, the charge stored in the capacitor 20 is discharged through the diode 17, the resistor 16, the junction between the gate and the cathode of the thyristor 13, and the resistor 14, allowing the thyristor 13 to conduct. As a result, the b direction voltage generated by the power generation winding 1 is brought to a short-circuit stage through the thyristor 13, the resistor 14 and the diode 15. In this way, the b direction voltage of the generation winding 1 is not applied to the capacitor 2, causing the ignition operation to stop. The voltage which flows across the resistor 14 at the time of bringing the b direction voltage to the short-circuit stage recharges the capacitor 20 through the diode 19, and the discharge as just mentioned is repeated. This allows the thyristor 13 to remain conductive stage even if the stop switch 11 is opened. In this way, a misfire state continues until the engine has stopped.
Since the conventional internal combustion engine stop device is constructed as described above, the a direction voltage generated by the power generation winding 1 is applied to the stop switch 11 through the diode 21, the capacitor 20 and the diode 22 during the operation of the engine, i.e. when the stop switch 11 is opened. This applied voltage is at a high level. As a result, there is a problem in that the reliability of the device is low because, for example, the stop circuit 12 can be actuated when a leakage current having an extremely small value flows between the contacts of the stop switch 11 due to the deterioration in insulating properties of the stop switch 11, the wiring and the like, or the presence of a droplet or dust on the stop switch 11.